The invention applies to the field of turbomachines and relates to a device for injecting a mixture of air and fuel into a combustion chamber of a turbomachine.
It relates more precisely to a novel type of assembly for an aerodynamic injection device.
In the remainder of the description, the terms “upstream” or “downstream” will be used to denote the positions of the structural elements in relation to one another in the axial direction, taking the gas flow direction as reference point. Likewise, the terms “internal” or “radially internal” and “external” or “radially external” will be used to denote the positions of the structural elements in relation to one another in the radial direction, taking the axis of rotation of the turbomachine as reference point.
A turbomachine comprises one or more compressors which deliver pressurized air to a combustion chamber, where the air is mixed with fuel and ignited so as to generate hot combustion gases. These gases flow downstream of the chamber toward one or more turbines, which convert the energy thus received in order to rotate the compressor or compressors and provide the work required, for example, to power an aircraft.
Typically, the combustion chambers used in aeronautics comprise an internal wall and an external wall interconnected at their upstream end by a chamber endwall. The chamber endwall has, spaced circumferentially, a plurality of openings each accommodating an injection device which allows the mixture of air and fuel to be fed into the chamber. Each injection device particularly comprises a fuel injector, radial swirl inducers, a venturi, a bowl and a deflector, which are interconnected, the chamber endwall being fastened to the deflector.
There are a number of combustion chamber types: “single-head” chambers, also referred to as “conventional” chambers, that is to say with a single circumferential row of injection devices, and “multi-head” chambers, that is to say with a plurality of circumferential rows of injection devices. Among the single-head chambers a distinction is drawn between chambers “with a reduced primary zone height” and conventional single-head chambers. The primary zone height corresponds to the distance between the internal wall and the external wall of the chamber, measured immediately downstream of the downstream end of a bowl.
In the case of a conventional single-head chamber, as illustrated in patent FR 2 753 779, the contact area between the bowl and the deflector generally forms a cylinder whose diameter is greater than the outside diameter of the swirl inducers.
In the following, as illustrated in FIG. 1, the reference D1 will denote the diameter of the cylinder corresponding to the contact area between the bowl and the deflector, and the reference D2 will denote the outside diameter of the swirl inducers.
In the case of a multi-head chamber or of a single-head chamber with a reduced primary zone height, the available space for the integration of the injection devices is smaller than for a conventional single-head chamber. The diameter D1 is therefore limited. However, it may be necessary with regard to some turbomachines to use “high-permeability” bowls in contrast to “conventional” bowls. The permeability is the capacity of an injection device to inject a certain air flow inside the bowl so as to create the desired mixture of air and fuel. High-permeability bowls are provided with swirl inducers whose inlet section is larger than in the case of conventional bowls. This leads to a larger axial bulk of the swirl inducers and also affects the radial bulk of the injection device which, for its part too, is larger than in the case of conventional bowls. The use of high-permeability bowls additionally requires that a sufficient supply of pressurized air is maintained at the air intake holes made in the bowl, downstream of the radial swirl inducers. In the case of a multi-head chamber or a single-head chamber with a reduced primary zone height, given that the diameter D1 is limited, the outside diameter D2 of the radial swirl inducers then becomes greater than D1, making it impossible to supply the air intake holes.